A Tale of Two Disks: Mapping the Milky Way with the Final Data Release of APOGEE

• Published in: The Astrophysical journal Vol. 954; no. 2; pp. 124 - 153
• Main Authors: Imig, Julie, Price, Cathryn, Holtzman, Jon A., Stone-Martinez, Alexander, Majewski, Steven R., Weinberg, David H., Johnson, Jennifer A., Allende Prieto, Carlos, Beaton, Rachael L., Beers, Timothy C., Bizyaev, Dmitry, Blanton, Michael R., Brownstein, Joel R., Cunha, Katia, Fernández-Trincado, José G., Feuillet, Diane K., Hasselquist, Sten, Hayes, Christian R., Jönsson, Henrik, Lane, Richard R., Lian, Jianhui, Mészáros, Szabolcs, Nidever, David L., Robin, Annie C., Shetrone, Matthew, Smith, Verne, Wilson, John C.
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 01.09.2023; IOP Publishing; American Astronomical Society
• Subjects: Age; Apogees; Astronomi, astrofysik och kosmologi; Astronomical models; Astronomy & Astrophysics; ASTRONOMY AND ASTROPHYSICS; Astronomy, Astrophysics and Cosmology; Astrophysics; Constraint modelling; Disks; Distribution functions; Fysik; Galactic abundances; Galactic archaeology; Galactic evolution; Galaxies; Galaxy distribution; Galaxy Milky Way evolution; Galaxy stellar content; Galaxy structure; Giant stars; Iron; Magnesium; Metallicity; Milky Way; Milky Way disk; Milky Way evolution; Milky Way formation; Milky Way Galaxy; Natural Sciences; Naturvetenskap; Physical Sciences; Red giant stars; Sciences of the Universe; Solar neighborhood; Stellar age; Stellar ages; Stellar evolution; Systematic errors; Vertical distribution; Milky Way formation; Astrophysics - Astrophysics of Galaxies; Galactic abundances; Galaxy structure; Milky Way Galaxy; Stellar ages; Milky Way evolution; Galactic archaeology; Milky Way disk; Galaxy stellar content
• ISSN: 0004-637X; 1538-4357; 1538-4357
• DOI: 10.3847/1538-4357/ace9b8

We present new maps of the Milky Way disk showing the distribution of metallicity ([Fe/H]), α -element abundances ([Mg/Fe]), and stellar age, using a sample of 66,496 red giant stars from the final data release (DR17) of the Apache Point Observatory Galactic Evolution Experiment survey. We measure radial and vertical gradients, quantify the distribution functions for age and metallicity, and explore chemical clock relations across the Milky Way for the low- α disk, high- α disk, and total population independently. The low- α disk exhibits a negative radial metallicity gradient of −0.06 ± 0.001 dex kpc −1 , which flattens with distance from the midplane. The high- α disk shows a flat radial gradient in metallicity and age across nearly all locations of the disk. The age and metallicity distribution functions shift from negatively skewed in the inner Galaxy to positively skewed at large radius. Significant bimodality in the [Mg/Fe]–[Fe/H] plane and in the [Mg/Fe]–age relation persist across the entire disk. The age estimates have typical uncertainties of ∼0.15 in log(age) and may be subject to additional systematic errors, which impose limitations on conclusions drawn from this sample. Nevertheless, these results act as critical constraints on galactic evolution models, constraining which physical processes played a dominant role in the formation of the Milky Way disk. We discuss how radial migration predicts many of the observed trends near the solar neighborhood and in the outer disk, but an additional more dramatic evolution history, such as the multi-infall model or a merger event, is needed to explain the chemical and age bimodality elsewhere in the Galaxy.